Continuous cardiac output monitoring by pulse contour during cardiac surgery

Most pulse contour methods are unreliable under changing haemodynamic conditions, because no corrections are made for pressure-dependent compliance and reflections of pressure waves. The pulse contour method of Wesseling includes such corrections. Four thermodilution measurements equally spread over the ventilatory cycle were used to calibrate and evaluate this pulse contour method. We designed a prototype incorporating a combination of the thermodilution method and pulse contour method and evaluated its potential for monitoring patients undergoing coronary bypass graft operation. Eight to 12 times during the operation, cardiac output was estimated by pulse contour and by thermodilution. The results were compared: the linear regression between the methods was COpc = 0.3 + 0.94. COth, (r = 0.94). The standard deviation for the difference between the methods against the mean of the methods was 10.6%. We concluded that the corrected pulse contour method estimates cardiac output accurately, even when heart rate, blood pressure, and total peripheral resistance change substantially.